One type of semiconductor package is referred to as a "multi chip module". These packages include semiconductor dice mounted directly to a substrate, such as a printed circuit board. The dice can be bare dice or contained in chip scale packages. In addition, the dice can be mounted in a chip-on-board configuration, or in a flip chip configuration. With chip-on-board mounting, the dice are back bonded to the substrate, and wire bonds are formed between the bond pads on the dice, and corresponding bonding sites on the substrate. With flip chip bonding, the dice are mounted circuit side down, with the bond pads on the dice soldered to solder wettable pads on the substrate.
Typically, a multi chip module will be arranged in a particular electronic configuration. For example, a single-in-line memory module (SIMM) can include an array of interconnected DRAMs, with edge connectors on the substrate that include dedicated input/output ports for the module.
Also with multi chip modules, an encapsulant layer can be used to protect and seal the dice on the substrate. For example, the encapsulant material can be applied directly to the dice and substrate in the form of a "glob top". Glob top encapsulation materials typically comprise electrically insulating polymers such as epoxies, silicones and polyimides. The glob top can be formed by dispensing a required volume of viscous material over the dice and portions of the substrate. A fence can also be formed on the substrate, as a mold for defining a perimeter of the glob top. The glob top can be formed over individual dice and associated wire bonds, or can be formed over groups of dice. Following dispensing, the encapsulation material can be cured at an elevated temperature (e.g. 165.degree. C.) for a suitable period of time (e.g. 60 minutes). Thereafter, the dice can be subjected to testing, to evaluate the electrical characteristics of the module prior to assembly in an electronic device.
One limitation of a glob top encapsulation process is that the curing process is relatively time consuming. This increases the length of the packaging process and decreases package throughput. Also, the glob top dispensing and curing apparatus can be relatively expensive to install and operate.
Another limitation of glob top encapsulation is that following encapsulation, the dice cannot be removed from the substrate. This essentially prevents defective dice from being replaced or repaired. Accordingly, some substrates are provided with one or more replacement sites on which replacement dice can be mounted. The defective dice are then electronically by-passed. However, replacement sites increase the size of the substrate and add expense to the module. Also the defective dice may sometimes be repairable but cannot be removed for repair because of the glob top.
In view of the foregoing, it would be advantageous to utilize a cover to protect and seal dice on a substrate, which can be easily removed to permit defective dice to be repaired or replaced. Accordingly, the present invention is directed to a semiconductor package that includes a pre-fabricated protective cover for dice mounted to a substrate. Still further, the present invention is directed a method for fabricating electronic assemblies, such as multi chip modules and BGA connects, that include one or more dice on a substrate.